Contribution of adventitial myofibroblasts to vascular remodeling and lesion formation after experimental angioplasty in pig coronary arteries

Extreme Diversity of the Human Vascular Mesenchymal Cell Landscape

Background Human mesenchymal cells are culprit factors in vascular (patho)physiology and are hallmarked by phenotypic and functional heterogeneity. At present, they are subdivided by classic umbrella terms, such as "fibroblasts," "myofibroblasts," "smooth muscle cells," "fibrocytes," "mesangial cells," and "pericytes." However, a discriminative marker-based subclassification has to date not been established. Methods and Results As a first effort toward a classification scheme, a systematic literature search was performed to identify the most commonly used phenotypical and functional protein markers for characterizing and classifying vascular mesenchymal cell subpopulation(s). We next applied immunohistochemistry and immunofluorescence to inventory the expression pattern of identified markers on human aorta specimens representing early, intermediate, and end stages of human atherosclerotic disease. Included markers comprise markers for mesenchymal lineage (vimentin, FSP-1 [fibroblast-specific protein-1]/S100A4, cluster of differentiation (CD) 90/thymocyte differentiation antigen 1, and FAP [fibroblast activation protein]), contractile/non-contractile phenotype (α-smooth muscle actin, smooth muscle myosin heavy chain, and nonmuscle myosin heavy chain), and auxiliary contractile markers (h1-Calponin, h-Caldesmon, Desmin, SM22α [smooth muscle protein 22α], non-muscle myosin heavy chain, smooth muscle myosin heavy chain, Smoothelin-B, α-Tropomyosin, and Telokin) or adhesion proteins (Paxillin and Vinculin). Vimentin classified as the most inclusive lineage marker. Subset markers did not separate along classic lines of smooth muscle cell, myofibroblast, or fibroblast, but showed clear temporal and spatial diversity. Strong indications were found for presence of stem cells/Endothelial-to-Mesenchymal cell Transition and fibrocytes in specific aspects of the human atherosclerotic process. Conclusions This systematic evaluation shows a highly diverse and dynamic landscape for the human vascular mesenchymal cell population that is not captured by the classic nomenclature. Our observations stress the need for a consensus multiparameter subclass designation along the lines of the cluster of differentiation classification for leucocytes.

Early adventitial activation characterized by NADPH oxidase expression and neovascularization in an aortic transplantation model

Increasing evidence has suggested that arterial adventitia may contribute to pathological vessel remodeling by producing reactive oxygen species and promoting neovascularization. However, these processes have not been studied yet in transplantation-induced vascular pathologies. We characterized the dynamic changes in NADPH oxidase expression and adventitial angiogenic response in a model of allograft aortic transplantation. The thoracic aorta from Fischer 344 rats were transplanted into the abdominal aorta of Lewis rats. Graft specimens were collected on days 0.5, 3, 7, and 14 for morphometry, immunohistochemistry, immunofluorescence staining, and quantitative PCR tests. Following transplantation, adventitial thickening was found as early as day 3, while neointima was observed from day 7. As compared to normal adventitial tissue, the expression levels of NADPH oxidase subunits gp91phox and p47phox in graft adventitia were elevated from day 3 and further increased up to day 14. Immunohistochemistry staining showed that infiltrating macrophages appeared to be a major source of NADPH oxidase expression. Increases in NADPH oxidase expression were also detected in fibroblasts isolated from the graft adventitia. Gene silencing of p47phox significantly suppressed proliferation and migration of the graft fibroblast cells. We also showed that adventitial thickening was accompanied by increased adventitial neovascularization; at day 14, there was a positive correlation between the density of adventitial microvessels and the neointimal thickness. Transplantation injury induces NADPH oxidase expression and neovascularization in the adventitia, raising the possibility that the activated adventitia may represent a target site for prevention of transplantation-induced transplant vasculopathy.

Myopericytoma and arterial intimal thickening: the relationship between myopericytes and myointimal cells

BACKGROUND

Myopericytomas with intravascular growth have been reported and have been occasionally documented as intraarterial. In a retrospective study, we assessed intraarterial growth in myopericytomas, co-existence with arterial intimal thickening (IT) and the relationship between the two.

METHODS

This retrospective study was undertaken using 11 myopericytomas evaluated in serial microscopical sections. The results in light microscopy, electron microscopy and immunohistochemistry [including α-smooth muscle actin (SMA), desmin and h-caldesmon] were evaluated.

RESULTS

In four myopericytomas, we found intraarterial growth, with large areas of disrupted arterial wall and attachment of veins and venules, exhibiting angiogenic phenomena. Arterial IT was present and partially incorporated within the tumor (simulating medium-sized vessels). The neointimal (myointimal) cells shared morphological and immunohistochemical phenotype with the myopericytoma myoid cells, including α-SMA positivity and desmin negativity. Four of the remaining myopericytomas showed structures similar to arterial IT within the tumor.

CONCLUSIONS

The findings shown here, including the association between myopericytomas and arterial IT, the incorporation of the latter into the tumor and the similar phenotype of their respective myoid and myointimal cells, support a close relationship between these processes. Histogenically, the pericytes of the penetrating neovasculature originating from the attached venules and veins may contribute to both lesions.

A unifying hypothesis for scleroderma: identifying a target cell for scleroderma

We propose that a recent change in the conception of the role of type 1 interferon and the identification of adventitial stem cells suggests a unifying hypothesis for scleroderma. This hypothesis begins with vasospasm. Vasospasm is fully reversible unless, as proposed here, the resulting ischemia leads to apoptosis and activation of type 1 interferon. The interferon, we propose, initiates immune amplification, including characteristic scleroderma-specific antibodies. We propose that the interferon also acts on adventitial stem cells, producing myofibroblasts, rarefaction, and intimal hyperplasia--three morphologic changes that characterize this disease. Regulator of G-protein signaling 5 (RGS5), a regulator of vasoactive G-protein-coupled receptors, is a cell type-specific marker of pericytes and scleroderma myofibroblasts. RGS5 may provide a key link between initial hyperplasia and fibrosis in this disease.

Role of myofibroblasts in vascular remodelling: focus on restenosis and aneurysm

Myofibroblasts (MFs) are contractile cells deriving from a multiplicity of resident cells and/or circulating progenitors that are known to play a key role in wound healing. They were first discovered and analysed in the early 1970s in granulation tissue. Since their first identification, the role of MF and their mechanisms of differentiation have been highlighted in a number of diseases, including organ fibrosis and tumours, with particular attention devoted to the liver, kidney, and pulmonary fibrosis. The aim of this review is to summarize the current evidence for the role played by MFs in two frequent vascular diseases related to the remodelling of the vascular wall: the different forms of arterial restenosis and the most common forms of thoracic aortic aneurysm. The in-depth knowledge of the molecular pathways involved in MF differentiation, contraction, and survival/apoptosis could contribute to the identification of novel therapeutic strategies for anti-fibrotic and anti-remodelling therapy of vascular diseases in which these cells are involved.

Neointimal hyperplasia associated with synthetic hemodialysis grafts

Stenosis is a major cause of failure of hemodialysis vascular grafts and is primarily caused by neointimal hyperplasia (NH) at the anastomoses. The objective of this article is to provide a scientific review of the biology underlying this disorder and a critical review of the state-of-the-art investigational preventive strategies in order to stimulate further research in this exciting area. The histology of the NH shows myofibroblasts (that are probably derived from adventitial fibroblasts), extracellular matrices, pro-inflammatory cells including foreign-body giant cells, a variety of growth factors and cytokines, and neovasculature. The contributing factors of the pathogenesis of NH include surgical trauma, bioincompatibility of the synthetic graft, and the various mechanical stresses that result from luminal hypertension and compliance mismatch between the vessel wall and graft. These mechanical stimuli are focal in nature and may have a significant influence on the preferential localization of the NH. Novel mechanical graft designs and local drug delivery strategies show promise in animal models in preventing graft NH development. Successful prevention of graft stenosis would provide a superior alternative to the native fistula as hemodialysis vascular access.

Urokinase-type plasminogen activator deficiency (uPA-KO) prevented carotid artery ligation-induced vascular remodeling in mice

It has been demonstrated that urokinase-type plasminogen activator (uPA) plays an important role in vascular remodeling. This study was designed to determine whether uPA deficiency (KO) affects carotid artery ligation-induced vessel remodeling and the interaction with angiotensin II (Ang II). Ligation of the left common carotid artery in 6-month-old wild-type (C57 black/6J) mice for 4 weeks induced a concentric remodeling with vessel wall thickening, characterized by cell proliferation in neointima, media, and adventitia, and with lumen narrowing without a significant enlargement of overall vessel dimension. Intima lesions were characterized by alpha-actin positive smooth muscle cell (SMC) proliferation in a matrix background. No detectable presence of MAC-3 positive macrophages existed in the vascular wall. The ligation-induced vascular neointimal formation and adventitial proliferation, but not lumen narrowing and media expansion, were completely prevented in age-matched uPA-KO mice. Chronic infusion of Ang II (1.44 mg/kg per day) via a subcutaneously implanted osmotic minipump did not significantly affect the gross morphology of the nonligated carotid artery from both wild-type and uPA-KO mice, but it enhanced ligation-induced vascular remodeling. However, in the presence of Ang II, uPA deficiency had no effects on ligation-induced mophermetric change, but it partially and significantly reduced cell proliferation. These data indicate that uPA may play a critical role in ligation-induced vessel remodeling. Ang II may activate other mechanisms independent of uPA to exacerbate ligation-induced vascular remodeling.

Application to Vascular Adventitia of a Nonviral Vector for TIMP-1 Gene Therapy to Prevent Intimal Hyperplasia

Somatic gene transfer continues to have potential for the study and therapy of cardiovascular disease. We have developed a modular, self-assembling, nonviral system consisting of Lipofectin, integrin-targeting peptides, and plasmid DNA (LID) and we have applied this to a model of vascular injury, rat carotid angioplasty. Marker gene studies identified transfection of adventitial cells after vector delivery to that layer. Human tissue inhibitor of metalloproteinase-1 (hTIMP-1) was tested as a therapeutic gene product after direct application to the exposed adventitial layer. Vascular LID.hTIMP-1 transfection was confirmed by polymerase chain reaction and gene expression by immunohistochemistry at 7 days. Neointimal areas were 0.160 +/- 0.078 and 0.225 +/- 0.052 mm(2) for LID.hTIMP-1-transfected (n = 14) and LID.pCI-transfected (n = 12) vessels, respectively, at 14 days, and 0.116 +/- 0.068 mm(2) (n = 14) and 0.194 +/- 0.095 mm(2) (n = 14), respectively, at 28 days, representing a 29 and 40% reduction in neointimal hyperplasia at 14 and 28 days, respectively, after balloon dilatation. Neointima-to-media ratios were similarly reduced. In addition, expansile remodeling after balloon injury was inhibited at 14 days, the area within the external elastic lamina being 0.50 +/- 0.02 and 0.61 +/- 0.02 mm(2) in LID.hTIMP-1- and LID.pCI-transfected arteries, respectively (p < 0.0005). We have demonstrated an effective system of therapeutic gene transfer, particularly targeting the arterial adventitia, where transfer of genes involved in matrix remodeling and cell migration may be useful.

Bisphosphonate-mediated gene vector delivery from the metal surfaces of stents

The clinical use of metallic expandable intravascular stents has resulted in improved therapeutic outcomes for coronary artery disease. However, arterial reobstruction after stenting, in-stent restenosis, remains an important problem. Gene therapy to treat in-stent restenosis by using gene vector delivery from the metallic stent surfaces has never been demonstrated. The present studies investigated the hypothesis that metal-bisphosphonate binding can enable site-specific gene vector delivery from metal surfaces. Polyallylamine bisphosphonate (PAA-BP) was synthesized by using Michael addition methodology. Exposure to aqueous solutions of PAA-BP resulted in the formation of a monomolecular bisphosphonate layer on metal alloy surfaces (steel, nitinol, and cobalt-chromium), as demonstrated by x-ray photoelectron spectroscopy. Surface-bound PAA-BP enabled adenoviral (Ad) tethering due to covalent thiol-binding of either anti-Ad antibody or a recombinant Ad-receptor protein, D1. In arterial smooth muscle cell cultures, alloy samples configured with surface-tethered Ad were demonstrated to achieve site-specific transduction with a reporter gene, (GFP). Rat carotid stent angioplasties using metal stents exposed to aqueous PAA-BP and derivatized with anti-knob antibody or D1 resulted in extensive localized Ad-GFP expression in the arterial wall. In a separate study with a model therapeutic vector, Ad-inducible nitric oxide synthase (iNOS) attached to the bisphosphonate-treated metal stent surface via D1, significant inhibition of restenosis was demonstrated (neointimal/media ratio 1.68 +/- 0.27 and 3.4 +/- 0.35; Ad-iNOS vs. control, P < 0.01). It is concluded that effective gene vector delivery from metallic stent surfaces can be achieved by using this approach.

Reactive oxygen species in the vasculature: molecular and cellular mechanisms

Accumulating evidence indicates that reactive oxygen species (ROS) play major roles in the initiation and progression of cardiovascular dysfunction associated with diseases such as hyperlipidemia, diabetes mellitus, hypertension, ischemic heart disease, and chronic heart failure. ROS produced by migrating inflammatory cells as well as vascular cells (endothelial cells, vascular smooth muscle cells, and adventitial fibroblasts) have distinct functional effects on each cell type. These include cell growth, apoptosis, migration, inflammatory gene expression, and matrix regulation. ROS, by regulating vascular cell function, can play a central role in normal vascular physiology, and can contribute substantially to the development of vascular disease.

Local infusion of the nitric oxide donor Sin-1 after angioplasty. Effects on intimal hyperplasia in porcine coronary arteries

PURPOSE

To investigate the development of intimal hyperplasia in response to percutaneous transluminal coronary angioplasty (PTCA) followed by local delivery of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1).

MATERIAL AND METHODS

Overdilation PTCA was performed in coronary arteries in 20 healthy pigs. One of the dilated segments was additionally treated with local delivery of SIN-1 for 10 min. Segments distal to the treated part of the arteries served as controls. Arteries were radiographically depicted and analyzed after 1 and 8 weeks for actin, myosin and intermediate filaments (IF), nitric oxide synthetase (NOS) and histological evaluation.

RESULTS

Segments treated with PTCA+SIN-1 showed a significantly (p=0.03) larger luminal diameter compared with PTCA only treated segments. The luminal loss after SIN-1 was not significant compared with the diameter prior to treatment. Endothelial NOS content was significantly lower in the PTCA+SIN-1 group compared with the PTCA group after 1 (p=0.03) and 8 weeks (p=0.013). IF/actin ratio after 1 week was significantly increased in PTCA-treated segments compared with untreated controls (p=0.004), and compared with PTCA+SIN-1-treated segments (p=0.004).

CONCLUSION

PTCA-induced intimal hyperplasia was potently inhibited by local delivery of the NO donor SIN-1. Momentary events at the time of injury play a significant role in the development of intimal hyperplasia and long-lasting down-regulation of the endothelial NOS expression after SIN-1 exposure is suggested. The IF/actin ratio can be useful as an early marker of intimal hyperplasia.

Different alpha-adrenoceptors mediate migration of vascular smooth muscle cells and adventitial fibroblasts in vitro

Norepinephrine directly induces growth of the vascular wall, which may involve not only proliferation of smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) but also augmentation of their migration. To test this hypothesis, growth-arrested SMCs and AFBs from rat aorta were exposed to norepinephrine. Norepinephrine caused dose-dependent migration of both cell types that was dependent on chemotaxis. In contrast, platelet-derived growth factor (PDGF)-BB, used as a positive control, stimulated both chemotaxis and chemokinesis. Only alpha(1D)-adrenoceptors (AR) and alpha(2)-AR antagonists inhibited norepinephrine migration of SMCs, whereas norepinephrine migration of AFBs was only inhibited by alpha(1A)-AR and alpha(1B)-AR antagonists; beta-AR blockade was without effect. Norepinephrine and PDGF-BB were additive for AFB, but not SMC, migration. Stimulation of migration was reversed at high norepinephrine concentrations (10 microM); this inhibition was mediated by alpha(2)- and beta-ARs in AFBs but not in SMCs. Thus norepinephrine induces migration of SMCs and AFBs via different alpha-ARs. This action may participate in wall remodeling and norepinephrine potentiation of injury-induced intimal lesion growth.

Trophic effect of norepinephrine on arterial intima-media and adventitia is augmented by injury and mediated by different alpha1-adrenoceptor subtypes

In vivo studies have suggested that norepinephrine (NE) directly contributes to normal vascular wall growth and worsening of hypertrophy, atherosclerosis, and restenosis. However, it is unknown whether these effects are secondary to hemodynamic changes caused by systemic NE or alpha-adrenoceptor (AR) antagonists. Herein, we determined if NE directly stimulates growth of medial smooth muscle cells (SMCs) and adventitial fibroblasts (AFBs) that we have shown express alpha1-ARs in similar abundance. The rat aorta was isolated before injury, 4 days after, or 12 days after balloon injury, and maintained under circumferential tension in organ culture for 48 hours with 1 micromol/L NE. Intima-media and adventitia were separated and DNA content, protein synthesis, and protein content measured. In uninjured aorta, NE increased DNA and protein content similarly in adventitia, and increased only protein content in intima-media, suggesting AFB proliferation and SMC hypertrophy. In vessels isolated 4 or 12 days after injury, NE increased all 3 endpoints in both layers by up to 20-fold greater than in uninjured vessels. These effects were dose-dependent and were unaffected by alpha2- or beta-AR blockade (except increased DNA content in adventitia that was also inhibited by alpha2-AR blockade). Intima-media growth was blocked by KMD3213 (alpha1A-AR antagonist) and adventitial growth by AH11110A (alpha1B-AR antagonist), whereas BMY7378 (alpha1D-AR antagonist) had no effect. NE decreased SMC marker proteins (eg, alpha-smooth muscle actin and desmin) and augmented the changes induced by injury. These data suggest that prolonged stimulation of alpha1A- and alpha1B-ARs induces growth of SMCs and AFBs, respectively, that is significantly augmented by injury.

Formulation and delivery mode affect disposition and activity of tyrphostin-loaded nanoparticles in the rat carotid model

Poor drug residence in the arterial wall hinders clinical implementation of local drug delivery strategies for the treatment of restenosis. A rat carotid model of vascular injury and intraluminal delivery of tyrphostin-containing polylactic acid (PLA) nanoparticles (NPs) were used to determine the relationship between residence properties and biological activity of different formulations and administration modes. The effects of delivery modes (denudation and delivery time) and formulation variables (adsorbed vs encapsulated drug, and NP size) on arterial drug/NP retention were examined. Antirestenotic effects of large (160 nm) and small (90 nm) tyrphostin-containing NPs, surface-absorbed tyrphostin, and systemic treatment were compared. Fluorescent NPs were used to study the spatial distribution of the carrier in the arterial wall. The decrease in arterial tyrphostin level over time fitted a biexponential model. Delivery time and pressure, endothelium integrity, particle size, and drug-polymer association affected local pharmacokinetics and the antirestenotic results after 14 days. The PLA-based tyrphostin NP formulation ensured a prolonged drug residence at the angioplasty site after single intraluminal application. Several readily adjustable formulation and procedural factors considerably modified arterial ingress of the drug-loaded NPs and governed their subsequent redistribution, tissue binding, elimination, and ensuing antirestenotic effect.

Invited review: cGMP-dependent protein kinase signaling mechanisms in smooth muscle: from the regulation of tone to gene expression

cGMP is a second messenger that produces its effects by interacting with intracellular receptor proteins. In smooth muscle cells, one of the major receptors for cGMP is the serine/threonine protein kinase, cGMP-dependent protein kinase (PKG). PKG has been shown to catalyze the phosphorylation of a number of physiologically relevant proteins whose function it is to regulate the contractile activity of the smooth muscle cell. These include proteins that regulate free intracellular calcium levels, the cytoskeleton, and the phosphorylation state of the regulatory light chain of smooth muscle myosin. Other studies have shown that vascular smooth muscle cells (VSMCs) that are cultured in vitro may cease to express PKG and will, coincidentally, acquire a noncontractile, synthetic phenotype. The restoration of PKG expression to the synthetic phenotype VSMC results in the cells acquiring a more contractile phenotype. These more recent studies suggest that PKG controls VSMC gene expression that, in turn, regulates phenotypic modulation of the cells. Therefore, the regulation of PKG gene expression appears to be linked to phenotypic modulation of VSMC. Because several vascular disorders are related to the accumulation of synthetic, fibroproliferative VSMC in the vessel wall, it is likely that changes in the activity of the nitric oxide/cGMP/PKG pathway is involved the development of these diseases.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

Integrin alpha(v)beta(3) is involved in stimulated migration of vascular adventitial fibroblasts by basic fibroblast growth factor but not platelet-derived growth factor

We examined the effects of basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) on the migration of vascular adventitial fibroblasts (VAFs) isolated from rat aortic adventitiae. Both bFGF and PDGF significantly stimulated VAF migration in vitro. An antibody to rat beta(3) integrin reduced bFGF-stimulated migration in a dose dependent manner. Moreover, VAF migration was inhibited in the presence of cyclic RGD (cRGD) peptide. However, PDGF-directed migration was blocked only by equivalent cRGD peptide but not by antibody to beta(3) integrin. These data suggest that alpha(v)beta(3) integrin mediates VAF migration stimulated by bFGF and that chemoattractant directed migration may be through distinct integrins.

Remodeling of carotid artery is associated with increased expression of matrix metalloproteinases in mouse blood flow cessation model

BACKGROUND

The matrix-degrading activity of matrix metalloproteinases (MMPs), required for cell migration and general tissue reshaping, is thought essential for pathological arterial remodeling in atherosclerosis and restenosis.

METHODS AND RESULTS

We triggered remodeling of the carotid artery in C57BL/6 mice by blood flow cessation to study the relationship with gelatinases MMP-9 and MMP-2. Ligated and contralateral carotid arteries from ligated and sham-operated mice were harvested fresh, for biochemical analyses, or were perfusion-fixed, for histological studies, at 0, 1, 3, 7, 14, and 28 days after ligation. An early statistically significant (P:<0.01) 4- to 5-fold increase in MMP-9 expression detected by SDS-PAGE zymography and Western blotting in tissue homogenates of ligated carotid arteries 1 day after flow cessation was maintained through day 7, after which expression gradually fell. Maximal MMP-9 levels were higher than MMP-2 levels, which became significantly increased 7 days after ligation. Proliferating cells, identified by bromodeoxyuridine incorporation, were detectable at day 1 in the adventitia and subsequently throughout the wall. Neointima was visible in 3-day specimens of ligated arteries. Suggested by morphology and predicted by theoretical considerations, maximal MMP-9 expression coincided with cell migration into the neointima, supporting its enabling role. Morphological measurements also demonstrated positive lumen remodeling up to 7 days after ligation.

CONCLUSIONS

MMP-9 induction is associated with the formation of intimal hyperplasia and does not require frank mechanical injury. Our data also show that a significant increase in MMP-9 expression preceded the positive geometrical remodeling of arteries, suggesting a potentially beneficial role for this matrix-degrading enzyme.

Kinetics of release of heparin from alginate hydrogel

PURPOSE

Injected sodium alginate may be a useful perivascular drug delivery vehicle. This study was performed to determine the release rates of heparin from sodium alginate hydrogels cross-linked with varying amounts of calcium gluconate.

MATERIALS AND METHODS

Six hydrogels, composed of 0.16 mEq sodium alginate and 4,000 units unfractionated heparin, were cross-linked with calcium gluconate to yield ion equivalence (IE) ratios (calcium:alginate) of 0.2, 0.4, 0.58, 0.8, 1.0, or 1.2. Two milliliters of normal saline was placed on top of each gel and allowed to remain in contact for up to 10 days. At set time intervals, the amount of heparin in the eluent was determined with use of high-performance liquid chromatography.

RESULTS

Gels with 0.2 and 0.4 IE were partially liquid at 24 hours; the other gels solidified within 10 minutes. The 0.58 IE gel was slowest to solidify but immobilized the most heparin and released heparin slowest over 10 days. At 10 days, between 5.5% and 9.8% of the heparin immobilized was retained in the gel.

CONCLUSION

This hydrogel shows promise as a vehicle for in vivo perivascular heparin delivery. The 0.58:1 IE ratio hydrogel has slowest release rate and the greatest immobilization despite its longer cross-linking time.

Urokinase stimulates differentiation of fibroblasts into myofibroblasts and their proliferation in damaged adventitia

Urokinase expression in the adventitia of rat common carotid artery increased on the 4th day after periadventitial damage. Periadventitial application of recombinant urokinase increased the area of the adventitia and the content of contractile and proliferating cells, while proteolytically inactive recombinant urokinase was ineffective.

Pathology of in-stent restenosis

The process of in-stent restenosis parallels wound healing responses. Stent deployment results in early thrombus deposition and acute inflammation, granulation tissue development, and ultimately smooth muscle cell proliferation and extracellular matrix synthesis. The severity of arterial injury during stent placement correlates with increased inflammation and late neointimal growth. These pathological findings provide useful targets for therapies aimed at reducing the incidence of in-stent restenosis.

Use of endothelial cells containing superparamagnetic microspheres to improve endothelial cell delivery to arterial surfaces after angioplasty

PURPOSE

The purpose of this study was to determine if the luminal surface of balloon-dilated arteries can be re-endothelialized circumferentially with use of normal endothelial cells (ECs) and superparamagnetic microsphere-containing endothelial cells (MagECs) to cover gravity-dependent and independent arterial surfaces, respectively.

MATERIALS AND METHODS

MagECs were obtained after phagocytosis of albumin-coated superparamagnetic polystyrene microspheres by rabbit microvascular ECs. The effect of microsphere internalization on cell adhesion was determined in vitro by comparing ECs and MagECs in terms of time courses of adhesion to fibronectin and cell retention after exposure to a shear stress. In vivo re-endothelialization was performed by delivering fluorescently labeled ECs and MagECs to a balloon-dilated artery with a double-balloon catheter, placing a magnet over the artery, and rotating the rabbit axially. Endoluminal coverage of arterial cross-sections was estimated by epifluorescence microscopy.

RESULTS

Under the influence of gravity, in vitro cell adhesion to fibronectin after 5, 10, and 15 minutes was similar for the ECs (34%, 74%, and 70%) and MagECs (40%, 56%, and 93%). In vitro cell retention after exposure to a shear stress (25 dynes/cm2) was greater (P < .05) for ECs than for MagECs (82% vs 69%). Use of ECs plus MagECs in vivo resulted in cell delivery that was nearly circumferential.

CONCLUSIONS

Delivery of a mixture of ECs and MagECs in combination with animal rotation and a magnetic field provide nearly circumferential delivery of ECs to the luminal surface of balloon-dilated arteries. The presence of superparamagnetic microspheres in cells does not impede cell adhesion but does decrease cell retention after exposure to a fluid shear.